Here's a critique of Libertarianism (not the same one I posted above, in fact) with an answer to that:

http://world.std.com/~mhuben/faq.html

> If you don't pay your taxes, men with guns will show up at your house, initiate force and put you in jail.

> This is not initiation of force. It is enforcement of contract, in this case an explicit social contract. Many libertarians make a big deal of "men with guns" enforcing laws, yet try to overlook the fact that "men with guns" are the basis of enforcement of any complete social system. Even if libertarians reduced all law to "don't commit fraud or initiate force", they would still enforce with guns.

If you don't like this contract, you can vote to change it.

If you can't get enough people on board to change it and you still don't like it, you can leave.